linux-kernel - Re: [PATCH] tracing: Fix possible crash in ftrace_free_ftrace

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Message-ID: <CAEr6+EC+Kg4AJ=BFxrOSQV+KHj5WSm=1FtYCAPrn1gFnZUk-fg@mail.gmail.com>
Date:   Mon, 9 May 2022 09:33:44 +0800
From:   Jeff Xie <xiehuan09@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     mingo@...hat.com, Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Fix possible crash in ftrace_free_ftrace_ops()

I am so sorry to bother you, this may be an invalid patch, kfree can
return directly from null. ;-)

On Mon, May 9, 2022 at 12:18 AM Jeff Xie <xiehuan09@...il.com> wrote:
>
> Currently if the ftrace_allocate_ftrace_ops() return -ENOMEM,
> the ftrace_free_ftrace_ops() will kfree(NULL).
>
> trace_array_create()
> {
>         ...
>         if (ftrace_allocate_ftrace_ops(tr) < 0)
>                 goto out_free_tr;
>         ...
> out_free_tr:
>         ftrace_free_ftrace_ops(tr);
>         ...
> }
>
> ftrace_allocate_ftrace_ops()
> {
>         ...
>         ops = kzalloc(sizeof(*ops), GFP_KERNEL);
>         if (!ops)
>                 return -ENOMEM;
>         ...
> }
>
> ftrace_free_ftrace_ops()
> {
>         kfree(tr->ops);
>         tr->ops = NULL;
> }
>
> Signed-off-by: Jeff Xie <xiehuan09@...il.com>
> ---
>  kernel/trace/trace_functions.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
> index 9f1bfbe105e8..d186d6101695 100644
> --- a/kernel/trace/trace_functions.c
> +++ b/kernel/trace/trace_functions.c
> @@ -73,6 +73,9 @@ int ftrace_allocate_ftrace_ops(struct trace_array *tr)
>
>  void ftrace_free_ftrace_ops(struct trace_array *tr)
>  {
> +       if (!tr->ops)
> +               return;
> +
>         kfree(tr->ops);
>         tr->ops = NULL;
>  }
> --
> 2.25.1
>

Thanks,
JeffXie